1. Field of the Invention
The invention relates to a method for recovering fine sand from equipment in the form of a floating grab-bucket conveyor or floating bucket chain dredging craft, whereby the dredged material is dewatered and conveyed to shore via floating conveyor belts.
In addition, the invention relates to a device for carrying out the method, by which the dredged material can be transferred to a dewatering screening machine with a material conveyor and floating belt arranged downstream, whereby the screening machine has a dewatering deck with a dewatering coating.
2. Description of the Prior Art
This floating equipment, which includes a bucket chain excavator or floating grab-bucket dredger, collects gravel under water and transports it to shore via floating conveyor belts. This gravel material must be dewatered before it is transported with conveyor belts. Therefore, dewatering is accomplished with a horizontal dewatering screen, on floating dredgers and floating bucket chain excavators. The dewatering screen is installed so that there is as little lifting height as necessary for the floating dredger, and as little conveyance height as possible is required for the bucket chain. Thus, the dewatering screen has to be built as low as possible. The material that is dewatered is transferred from the dewatering screen via a chute to the conveyor belt line transporting the material to shore.
Due to the dewatering slots, fine sand is lost together with the water in the dewatering process. This fine sand is returned to the water being dredged. Rather than return the fine sand, it can be recovered. A screening tub is employed for this purpose for collecting the material draining off. This screening tub is required because of the mandatory installation of the dewatering screen. This screening tub is provided with a pump, which pumps the material into a cyclone for the recovery. When sand is present in small amounts, the cyclone may selectively transfer the sand to the same dewatering machine, or if much fine sand is lost, it can transfer it to a second screen for transport to the conveyor belts.
The significant drawback of this method, which is known, from German design patent DE-GM 75 41 007, is that the energy consumption is increased by a solid pump employed for pumping the sand-and-water mixture into the cyclones with the required pressure. The device is characterized by high mechanical wear and high weight, which has a negative effect on the floating unit, and which requires high investment costs.
Therefore, it would be desirable to provide a method or device that reduces the energy requirement, weight and wear costs of the device.
The problems of the prior art are solved by installing a blind bottom below the dewatering screen of a screening machine. This blind bottom collects the water/fine sand mixture, discharges it into the conveyor device, and loads it in a washing trough acting as the separation bed of a hydro belt separator.
This blind bottom is located under the dewatering deck, and covers the entire surface area. In this case, the end zone viewed in the direction of conveyance has a discharge that is directed at a hydro belt separator consisting of a revolving endless conveyor belt with a washing trough acting as the separation bed, and an ascending part leading away from the washing trough. Thus, the conveyor belt runs in the direction of the ascent so that at the discharge of the screening machine, the dredged material is transferred to the washing trough of the hydro belt separator.
In an advantageous embodiment, the dewatering deck is designed as a classifying deck. This makes it possible to separate the complete sand fraction of, e.g. 0.2 mm, and to separate on the floating dredger the component of finest sand as well as organic components. In addition, there is a dewatering screen that is arranged below the ascending part of the conveyor belt. Furthermore, a return line runs from the dewatering screen to the hydro belt separator. Finally, there is also a filter that is arranged against the overflow of the separation bed.